Our kitchen sink vent pipe goes up through the ceiling but not through the roof, should it go through the roof?
This is actually pretty easy to remedy given that you have decent attic access. You just route vent to the main stack. Might have to cut out main stack in attic, support it, add a T to connect vent and put the pieces back together. That would be easy way to code compliance and could cost as little as $30-40.
If there is a main Vent stack in the house, then just route and connect it to it. Just be sure that you have your 1/4" per foot drop from end to end. We routed all front of the house vents to a Main stack in the back of the house. The only other issue you want to be aware of is the exit main stack should be as big as the sewer exit line. so if you have a 4" sewer, your stack should be at least 4". If not you should be adding a new stack. Leaking sewer gases in the Attic is not a good thing. You can downsize the vent one size from the drain it is connected it. If combining, you would need to look up the code to get the proper sizing.